Ignition spark gap device



' July 23, 1946 A. w. ROBINSON, JR" 2 4,658

IGNITION SPARK GAP DEVICE Filed April e, 1945 His Attorney- Patented July 23,1946

IGNITION SPARK GAP DEVICE Arthur W. Robinson, Jr., Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 6, 1943, Serial No. 482,036

1 Claim.

an electrical breakdown discharge at substantially a predetermined voltage.

Further objects and advantages of my invention will become apparent and my invention will be better understood from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claim annexed to and forming part of this specification.

In the drawing, Fig, 1 is an elevational view, partly broken away, illustrating an embodiment of my invention; Fig. 2 is a plan view, partly broken away along line 2-2 of Fig. 1; and Fig. 3 is a fragmentary sectional view of a part of a discharge electrode and its enclosing casing prior to the final step of assembly of an electrode in its casing.

Referring to the drawing, I have shown a quenched spark gap device adapted to be used in an ignition system which includes a pair of spaced apart electrodes having main body portions I and II each formed with an annular groove I2 in one of the faces thereof. This forms a central discharge portion l3 on each electrode, and a discharge face Id of suitable relatively hard electrically conductive material, such as tungsten, silver, or carbon, is fused, plated, or otherwise suitably secured to the central discharge portion I3. In order to obtain an accurate spacing-between adjacent discharge faces, the discharge electrode is formed by suitably grinding or otherwise finishing the outer plane surface of the discharge face I4 and the outer plane surface of a supporting flange I5 formed on the outer side of the groove I2, such that these outer surfaces both lie in the same plane. The desired predetermined spacing between the discharge faces I4 is obtained by arranging two discharge electrodes with the faces I4 thereof adjacent each other and spaced apart by an annular insulating element of substantially predetermined thickness arranged intermediate the faces of the flanges I5. This insulating spacing element I6 is formed of a suitable material, such as mica, and

2 extends from substantially the outer periphery of the electrodes to a short distance beyond the outer edges of the grooves I4, and the two electrodes and the spacing element iii are held in the desired relative axial relationship by an annular insulating spacer I'I arranged about the outer periphery of these elements. An enclosing casing is formed about the discharge electrodes and includes a substantially cup-shaped casing member I8 arranged about the spacer ll and each respective electrode. Each electrode is electrically connected and is secured to its respective casing I8 by being welded thereto at I9. This welded connection is made by forming the outer edge 20 of each electrode with a relatively small projection 2| which is arranged in engagement with the inner surface of the casing I8. In assembling the electrode in the casing, a welding terminal is connected to the electrode I0 and another welding terminal is connected to the outside of easing I8, such that welding current passes therebetween through the projection 2|, so as to heat this projection. Pressure is applied to the casing I8 and the electrode I0 so as to provide a suitable weld between the flange 20 of the electrode and the casing I8, as shown at III in Fig. 1. A pair of electrodes and casings then is assembled with a spacer element I6 between the outer portion of adjacent faces thereof to space apart these faces substantially a predetermined distance and with a spacer I'I arranged between the discharge electrode and the casing I8. Pressure is then applied to the outer side of the casings I8 to hold these casings in position and biases them towards each other and to bias the electrodes toward the intermediate insulating spacer element I6. The adjacent edges of these casings are then hermetically sealed together by a suitable insulating seal formed of an annular glass element 22 fused about the outer edges 23 of the casings. Due to manufacturing tolerances, it is substantially impossible to obtain a uniformly satisfactory predetermined spacing between the discharge faces I 4 in such an assembly. It is desirable, therefore, that this spacing be made as accurately as possible and that the pressure of the gas within the spark gap device be regulated such that the discharge between the faces I4 will take place at a substantially predetermined voltage. It is also desirable that a substantially pure and inert gas be used to fill the space within the spark gap device in order to minimize pitting of the discharge faces. This is obtained by evacuating the device through an opening 24 formed in one of the casings I8 and filling the device with a suitable gas, such as hydrogen, neon, or argon, then evacuating the device a second time and refilling it with the same gas. The opening 24 then is hermetically sealed in any suitable manner, as by welding at 25, to insure against the exchange of gas between the surrounding atmosphere and the inside of the discharge device. The pressure of the gas in the device is regulated such that with the spacing between the discharge faces, electrical discharge breakdown occurs between the discharge A quenched spark gap device including apair V of spaced apart electrodes each having an ancharge portions, an insulating spacer about the outer periphery of said electrodes, a cup-shaped faces between 1175 and 1225 peak volts of an al- N ternating current voltage or any other suitable predetermined voltage. In this manner, a uniform breakdown voltage is assured irrespective of variations in the manufacturing tolerances of the different elements used in each spark discharge device.

While I have illustrated and described a particular embodiment of my invention, modifications thereof will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not to be limited to the particular arrangement disclosed, and I intend in the appended claim to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

enclosing casing about said insulating spacer and each of said electrodes, each of said casings being welded to its respective electrode providing an electrical connection therebetween; means in-' cluding an annular gas-tight glass seal about the adjacent ends of said cup-shaped casings for substantially hermetically sealing said device with said casings insulated from each other and for holding said casings biased toward each other to maintain said electrodes biased toward said intermediate insulating element, and hydrogen gas in said device at a pressure such that electrical discharge breakdown between said discharge faces at the spacing therebetween occurs at between 1175 and .1225 peak volts of an alternating current voltage. V

' ARTHUR W. ROBINSON, JR. 

